Aluminum alloy



United States Patent 3370943 ALUMINUM ALLOY Earl C. Beatty and Frank L. Howard, Spokane, Wash,

assignors to Kaiser Aluminum & Chemical Corporation, ()akiand, Calif a corporation of Delaware No Drawing. Filed Nov. 4, 1965, Ser. No. 506,396 4 Ciaims. (Cl. 75-142) ABSTRACT OF THE DTSCLGSURE This specification discloses an alloy suitable for extrusion and for color anodizing and the process for forming a colored coating on such extrusion. The alloy has a composition of 6063 alloy to which from 0.15 to 0.5% copper and a preferred range of from 0.1 to 0.2% manganese is added.

This invention relates to a process for producing colored anodic oxide coatings on aluminum extrusions, and to an aluminum alloy adapted to receive such coatings.

It is now well known to color-anodize aluminum by processes that produce integrally colored coatings, as distinguished from colorless coatings that are later dyed or pigmented. Color-anodizing processes employ aqueous electrolytes containing sulfate ions and any of certain aromatic sulfonic acids that are substituted with hydroxyl or carboxyl groups or combinations of hydroxyl and carboxyl groups. When aluminum is employed as the anode in an electric circuit that includes the electrolyte, integrally colored anodic oxide coatings may be formed in colors ranging from light gold to black. The process may be applied to virtually any form of aluminum, but it is most often applied to sheets and extrusions, particularly sheets and extrusions employed for architectural purposes. This invention deals with such integrally colored coatings, and the term color-anodized or terms of similar import refer to integrally colored coatings.

Although it is easy, on a laboratory scale, to produce colored anodic oxide coatings, many difiicultics arise when producing them for commerce. Among these difficulties are producing a series of color-anodized articles that match. For example, it is difficult repeatedly to produce a number of color-anodized extrusions which have the same color, texture, and glossiness; in other words, the same appearance so that when used side by side they will match one another. Another problem is to create colors that are usable with one another even though the alloys employed are diiierent. Typical of this problem is employing color-anodized sheets as curtain walls in conjunction with color-anodized extrusions employed as door frames, spandrels, lintels, column sheaths or similar members.

Metals suitable for extrusion usually have a different composition than metals suitable for rolling, and they respond differently to anodizing conditions. Even a series of articles made of the same metal may respond to anodizing differently due to different microstructures. A series of extrusions may differ due to slight differences in the thermal treatment of the extrusion or the billet from which it is formed, and these differences in structure produce different appearing anodized extrusions even though the billets from which the extrusions were formed had identical composition.

Generally speaking, it is difficult to anodize to obtain darker colors on alloys that are constituted to be suitable for extrusion. For example, the alloy designated as 6063 alloy by the Aluminum Association is a widely used extrusion alloy and it is very difiicult to color-anodize with black or other dark coatings. Another difliculty is that the appearance of anodized 6063 alloy is extremely sensitive to the thermal treatments to which the alloy is subjected before and during extrusion. In this regard, it should be pointed out that control of thermal conditions is extremely difiicult. Even such a well known heat treatment as homogenizing can create difficulties because ingots are generally homogenized in groups piled one upon another so that both the heating and the cooling rate of ingots in the interior of the pile is substantially slower than the heating and cooling rates of ingots 0n the exterior of the pile thereby producing a different internal structure which in turn produces a different response to color-anodizing.

This invention provides an alloy suitable for extrusion and for accepting a range of color-anodized coatings; and to a method capable of producing rich colors ranging from light gold to dark colors on extruded aluminum and additionally it provides a method for reducing the effect that variations in thermal treatments have on the response an alloy has to an anodizing process. Stated differently, this invention provides a means for coloranodizing extruded products in such a Way that the color of the product will depend almost entirely on the composition of the metal and the program employed to anodize it thereby giving close control over reproducibility of appearance, and in addition it provides a means for obtaining dark colored and even black anodic oxide coatings on extrusions while still retaining the ability to make light colors.

The object of this invention is accomplished by providing an extrusion alloy containing from about 0.2 to about 0.6% silicon, up to 0.35% iron, from about 0.15 to about 0.5% copper, from about 0.1 to about 0.4% manganese, from about 0.4 to about 0.8% magnesium and the remainder substantially aluminum, preferably with the weight ratio of magnesium to silicon being between 1 and 2. A preferred alloy of this invention is one containing from about 0.3 %0 .4% siiicon, from about 0.l5%0.25% iron, from about 0.l5%-0.25% copper, from about 0.1%-0.2% manganese, from about 0.45%- 0.6% magnesium and the balance aluminum and normal impurities. All compositions stated in this specification and the following claims are on a weight percent basis unless stated otherwise.

The above-specified alloy is homogenized and formed into an extruded shape. The extruded shape is immersed as the anode in an aqueous electrolyte which contains in solution from about 0.1% to 4% sulfuric acid or the equivalent amount of sulfate ion and from about 0.09 to about 0.7 gram moles per liter of an organic sulfonic acid substituted with hydroxyl, carboxyl or combinations of hydroxyl and carboxyl groups. Suitable organic acids include but are not limited to sulfosalicyclic acid, sulfophthalic acid, sulforesorcinol, and lignosulfonic acid.

Anodizing is effected at conditions now well known to the color-anodizing art. The temperature of the electrolyte may range from near its freezing point to F. or substantially higher, the current density may range from about 10 to 100 amperes per square foot of surface being anodized, the voltage may range from about 30 to 130 volts and the time is that suflicient to produce the color and thickness of coating that is desired; usually less than minutes.

Following are several examples presented to illustrate the present invention with typical embodiments of it. The examples are intended to be illustrative and they have been selected as typical examples to demonstrate the invention rather than to limit it.

Extrusions were made from several alloys that are useful as extrusion alloys and capable of being coloranodized. Prior to anodizing the alloys were subjected to two tempers that differed substantially from one another in order to compare the difference in color-anodizing response caused by varying thermal treatments of an alloy prior to extrusion. The alloys were also anodized by two difierent electrical programs which are both characteristic of those employed to color-anodize extrusions.

The temper designated -T4 is one of the well known and standard tempers used through the aluminum industry with heat treatable aluminum alloys. The -T4 temper is obtained by solution heat treating and rapidly cooling the alloy after which it is aged at room temperature to a stable condition. The temper designated as -T6 is also a standard temper well known to the aluminum industry for use with a heat treatable alloy. It is imparted by solution treating an alloy after which it is artificially aged to approximately maximum tensile properties thereby producing a very strong and stable alloy.

The alloy shown in Table 2 as 6063 alloy is a typical example of the 6063 alloy designated in the Aluminum Association classification of alloys. The specific alloy used contained 0.36% silicon, 0.2% iron, 0.005% copper, 0.004% manganese, 0.6% magnesium, 0.005% chromium, 0.01% zinc, 0.004% titanium, and the remainder substantially aluminum containing normal amounts of impurities. The other alloys of the examples are the same 6063 composition with the specified amounts of additional elements. Thus, an alloy designated 6063 plus 0.4% manganese and 0.2% copper is the 6063 composition set forth above, but containing 0.4% manganese instead of 0.004% manganese and 0.2% copper instead of 0.004% copper.

In Table I two anodizing programs are set forth. The first anodizing program is employed in all cases in Example 1 and the second anodizing program is employed in all cases in Example 2. Examples 1 and 2 set forth the response to various anodizing treatments to the designated alloys in both the -T4 and the -T6 temper. The color reported for the -T4 temper is a subjective observation which is accomplished by comparing the colors obtained with previously established color standards. The colors obtained on the speciments with -T6 temper are comparative with respect to the colors on specimens with -T4 temper. Thus, if the T4 temper produces a bronze color and the -T6 temper produces a lighter bronze color, the color produced on the -T6 temper is reported as lighter with respect to the color produced on the specimen with a -T4 temper.

The following Table 1 sets forth the anodizing conditions employed in each of Examples 1 and 2:

TABLE 1 Example 1 Example 2 Sulfuric acid (grams/liter) 5 5 Sulfosalicylie acid (gram moles/liter) 0. 45 0. 45 Temperature F.) 75 75 Initial current density (amperes/sq. it.) 24 27 Maximum vol 65 60 Anodizing time (minutes) 40 45 Total current quantity (amp. hrs/sq. ft.)- 12.0 19

The results obtained in Example 1 are set forth in Table 2:

TABLE 2 T4 Temper T6 Temper Bronze Much lighter bronze. Dark bronze... Slightly lighter bronze. Black Very dark brown. Cu. do Black.

do Do.

4 ployed were radically different from one another and that they were selected to exaggerate anodizing response differences resulting from thermal history.

The results of anodizing under conditions set forth for Example 2 produced anodized alloys as set forth in Table 3 below:

Example 2 also illustrates that the combination of the manganese-copper-containing extrusion alloy and the color-anodizing process of this invention can produce darker colored anodized extrusions, and extrusions which are far less sensitive to their thermal history with respect to color-anodizing response.

Having thus described this invention, what is claimed is:

1. An alloy useful for producing color-anodized extrusions consisting essentially of from about 0.2% to about 0.6% silicon, up to about 0.35% iron, about 0.2% copper, about 0.4% manganese, from about 0.4% to about 0.8% magnesium and the remainder aluminum and normal impurities.

2. An alloy useful for producing color anodized extrusions consisting essentially of from about 0.2% to about 0.6% silicon, up to about 0.35% iron, from about 0.1% to about 0.2% manganese, from about 0.15% to about 0.5% copper, from about 0.4% to about 0.8% magnesium, the remainder, aluminum and normal impurities.

3. An alloy as described in claim 2 wherein the range of silicon is from about 0.3% to about 0.4%, the range of iron is from about 0.15% to about 0.25%, the range of copper is from about 0.15% to about 0.25%, and the range of magnesium is from about 0.45% to about 0.6%.

4. An alloy useful for producing color anodized extrusions consisting essentially of from about 0.2% to about 0.6% silicon, up to about 0.35% iron, from about 0.2% to about 0.4% manganese, from about 0.15% to about 0.5% copper, from about 0.4% to about 0.8% magnesium, the remainder, aluminum and normal impurities.

References Cited UNITED STATES PATENTS OTHER REFERENCES Glazov et al.: The Solubility of Certain Transition Elements in Aluminum, Metallovedenii i Term Obrabotka Metallov, No. 10 (1959).

Aluminum Association Alloy Designations, January 1967.

HOWARD S. WILLIAMS, Primary Examiner.

JOHN H. MACK, Examiner.

G. KAPLAN, Assistant Examiner. 

